Conventionally, in an image forming apparatus such as a copy machine, a printer, a facsimile, or the like, various types of rotary members are used. In order to cause such rotary members to rotate, it is required that a drive force be transmitted from a drive source such as a drive motor or the like to each of the rotary members, and to this end, a plurality of gears are used as a transmission member. As each of such gears, a resin gear is often used from the viewpoint of reductions in cost, noise, weight, and so on.
In a case of manufacturing a resin gear, as disclosed in, for example, Patent Document 1, generally, the gear is manufactured by injection molding using a mold in which a plurality of gates are disposed in a circumferential direction at an equal distance from each other.